1. Field of the Invention
The present invention relates to a reverse transcriptase enzyme from human milk, and its use in the detection of breast cancer.
2. Description of the Prior Art
The diagnosis of human cancer has been carried out in the prior art by detecting the presence of a variety of polypeptides in human sera.
Thus, for example, Bjorklund, U.S. Pat. No. 4,160,019 describes the isolation of a cancer associated polypeptide antigen (CAPA) showing monospecificity and being present in a wide variety of human cancers of different localizations. The material possessing CAPA activity is isolated by homogenizing malignant tissues from autopsies, carcinoma tissues of various types and sites being collected to make a tumor pool. The purified CAPA is a polypeptide based on the single peptide chain, soluble at a pH within the range of about 1-3.5, and denaturing irreversibly at pH's exceeding about 4.5. The antigen is hygroscopic, turns yellow and becomes inactivated and smeary when it takes up moisture. The authors established that CAPA originates from cancer cell walls. The polypeptide has a molecular weight within the range of 20,000-27,000 and does not contain any carbohydrate or nucleic acid. The presence of CAPA has been detected in cancers as varied as those originated in the intestines, colon, rectum, pancreas, breast, ovaries, prostate, testes, and the like.
Freedman et al, U.S. Pat. No. 3,663,684 describe a carcinoembryonic antigen showing so-called "CEA-activity". CEA is used for detection of cancer of the colon and is extracted from the antigen-containing tissues by a glycoprotein solvent. Its molecular weight is about 200,000, although it may be as low as 70,000. It is a glycoprotein.
Davidson et al, U.S. Pat. No. 4,146,603 also describe a class of glycoproteins found to be produced by human cancer cells and present in the sera of cancer patients. This glycoprotein is called "TSGP" (tumor specific glycoprotein). TSGP is generated by tumor cells regardless of the tumor concerned. It appears in the circulatory system of humans suffering from lung, mammary, colon, uterine, or gastric carcinomas, melanomas, and the like. It is used for the early diagnosis of individuals with any kind of malignant disease.
None of the aforementioned diagnostic tests is specific for breast cancer.
The presence of a reverse transcriptase enzyme in human breast cancer tissue has been established by Gerard, G. F. et al, Nature, 256: 140-143 (1975). In 1977, Ohno et al, Proceedings of the National Academy of Sciences, USA, 74: 764-768 (1977), described the properties of a reverse transcriptase purified from human breast cancer particles. This enzyme is a DNA polymerase with reverse transcriptase properties, sedimenting between 5 and 6 S and having a molecular weight estimated about 70,000. The enzyme was purified by fractionating breast tumor for particulate material of density 1.16-1.18 g/cm.sup.3, solubilizing this sample and applying it to a column of polyacrylamide agarose gel. Fractions containing the reverse transcriptase were then pooled and loaded onto a phosphocellulose column. The reverse transcriptase was then isolated by a fractionation on this column. Non-malignant samples yield no enzyme activity with the properties of the reverse transcriptase of Ohno et al. The reverse transcriptase from the Ohno et al preparation has been characterized immunologically and has been determined to be related to the reverse transcriptase of the Mason Pfizer monkey virus (Ohno et al, Proceedings of the National Academy of Sciences, USA, 74: 2144 (1977)).
Other studies (Schlom et al, Science, 175: 542 (1972), Dion, A. S. et al, Cancer Research 34: 3509 (1974), Feldman et al, Proceedings of the National Academy of Sciences, USA, 70: 1976 (1973)) have shown that some human milk samples contain RNA-dependent DNA nucleotidyl transferase activity (reverse transcriptase). The activity from human milk has, however, never been isolated, purified or immunologically characterized.
A need continues to exist for a rapid and efficient, as well as highly specific diagnostic test for the detection of human breast cancer. Such a test could be used for example, to qualify a generalized diagnosis of cancer (obtainable with the previously described tests) to a diagnosis of breast cancer.